For me it's an ironic story. As a kid, I cut the tags off (like destroysall)but then in middle school when I got my first part time job, I understood the keeping the tags on was important so I did so for my new purchases. But year after year of collecting, my collection has grown so large and keeping the figs clean is a pain in the ass but with the tags on, it's even worse. You fear to damage the tag when you run the figure in water for the hard to reach spots when air cans just can't get out. So about 3 years ago, I decided to pull the tags off as I will not sell my figures and removing the tags to make displays much cooler.
What I do is, use a hair dryer to warm up the tag hole and then pull it out. I then place the tags with those plastic hangers inside a photo album. By doing this, the tags will be preserved and the figures can be regularly cleaned without damaging the tags.
So like howze01, if in the future I decide to put the tags on, I'll just re-attach back into the original tag hole which could take days with this many Bandai figs.
If you're using the used car analogy, let's seller A has a tagged figure. It's in mint condition with no paint rubs or chips but the seller never cleaned it once so it's covered in dust. Seller B has a figure that's been cleaned and looks as mint as it can get but has a reattached the tag. Both list the item on eBay at the same time. Buyers will be more attracted to the clean figure versus the mint figure covered in dust. Even for used cars, don't they usually detail the car and make it shine before selling it to you?
I guess it really comes down to what kind of collector or seller you are and how much you value the figure being in it's complete original state. For me, I like clean figures as long as they are reasonably priced, with attached or unattached tags, and with no damage.